High-speed magnetic fluid clutch



Dec. 23, 1952 J. RABINOW HIGH-SPEED MAGNETIC FLUID CLUTCH INVENToR. Jacob Rahi'nmw Patented Dec. 23, 1952 UNITED STATES PATENT OFFICE HIGH-SPEED MAGNETIC FLUID CLUTCH `acob Rabinow, Takoma Park, Md., assignor to the United States of America as represented by the Secretary of the Army amended April 30, 1928; 370 O. G. 757) The invention described in the specification and claims may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

My invention relates to magnetic fluid clutches of the type employing a mixture of paramagnetic particles such as iron and a fluid vehicle such as oil, which, when subjected to a magnetic field, acts to transmit force between two otherwise independently movable members. This mixture will be referred to hereinafter as iron-oil for convenience, but it will be understood that any paramagnetic powder is contemplated, and any suitable fluid may be used. It will be further under- 2 the clutch. Formed on or aixed to end plate 5 is hollow shaft 6, which passes through bearing 2', and which contains journal bearing 'l in which shaft 8 may rotate. An O ring 9 provides an oil seal between end plate 5 and shaft 8. Mounted upon shaft 8 is clutch member Ill which is internal to chamber 4. Member I il is grooved to accommodate winding II which is of electrically insulated wire. A passageway I2 in member I0 and shaft 8 permits passage of a wire I3 which terminates in slip rings t4. A space as shown is left between member Il) and cup 4 to accommodate a mixture of iron powder and light oil. The mixture is so proportioned that only enough stood that the paramagnetic material may be l5 powder i5 t0 ill the Cylindrical sap ci' minimum used Without the fluid, peripheral space between member Il) and cup 4 It is known that the fluid in this clutch acts is used, the rest of the space including the radially chiefly as a lubricant and the magnetic action of extending gap J'Oiliing ntO tllc cylindrical gap the clutch is independent of the fluid used. Dry being Occupied by light Oil I5, or the oil may be paramagnetic particles alone have been successomitted in its entirety. When relative rotation fully used. exists between member It and cup 4, the iron In the art of magnetic fluid devices and more powder I5 and oil I6 become mixed, But when particularly of magnetic fluid clutches as derotational speed 0f cup 4 becomes so great that scribed in my copending applications, Serial No. appreciable centrifugal force is created, powder 51,402, filed September 21, 1948, and Serial No. I5 is urged outwardly so that onlyasmall amount 783,426, filed October 31, 1947, now Patent No. of drag upon member Id is produced, thus facili- 2,575,360 issued November 20, 1951, respectively, tating quick release of the clutch on de-energizait is desirable that the effects o-f centrifugal force tion thereof. be kept at a minimum so that the device will be Both member I0 and cup li are made of magcompletely responsive to changes in the current netic material. Thus, it will be seen that when used to actuate it. In conventional types 'of current is passed through coil II, magnetic poles magnetic fluid clutches, centrifugal force causes will be established at portions I'l and t8 of memthe iron particles in the iron-oil mixture to be er It and correspondingly at positions I9 and 20 impelled toward the periphery of the rotating of cup 4, the magnetic path or lines of magnetic chamber, and to become packed duc t0 tllc large 35 ux thus passing from I7 through powder I5 to radial head of iron particles. If rapid control is I9, thence to 2t, again through powder I5 and to be achieved, it is necessary that this condition returning to I8, so that the iron powder I5 will be overcome. To achieve this end I have inventbe attracted to path Il-I9 and path I8`20 with ed amdifled Olm Of BIBCIOmagIletC fluid CllltCh a, force depending upon the amount, 0f current in Which ai Small quantity Of magnetic pOWclcI' iS 40 passing through coil Il, and so controlling the used, aS ccmpalcfl With pliOl practice, aS Will be amount of rotational force transmitted from the apparent to one skilled in the art from reference driving member to the driven member, to the accompanying description and drawings, in Wi 13h reference now to Figure 2, Support-,S are Whcll provided for bearings 2, 2. Shaft 3 passes Figure 1 represents one form of electromagnetic 45 through bearing 2 supporting external cup 4 clutch of this type; which forms a chamber completed by end plate Figure 2 shows a second form of clectromag- 5 to which is aflixed or on which is formed hollow netic clutch of this type; and shaft 5 which passes through bearing 2', and in Figure 3 shows a differently filled clutch of this which bearing l is inserted to serve as a journal typg for shaft B. Packing 9 positioned between end Referring now to Figure 1, suitable supports I plate ii and shaft 8 serves as an oil seal. Memare provided to mount bearings 2, 2. A shaft 3 ber It, which is afxed to cup 4 and shaft 3, is rotates in bearing 2 and has formed upon or fixed shaped to accept an electrically insulated coil I I to its end a cup-shaped member 4, which togethpositioned approximately as shown. To the iner with end plate 5 forms ythe outer housing of 55 ternal end of shaft 8 is affixed internal cup 2l which is perforated with holes 22 to permit circulation of the iron-oil mixture I5, I6. It will be seen that cup 2| is positioned approximately midway between cup 4 and member I0. Shaft 3 and member III are provided with a passageway I2 to accommodate lead wires I3 which terminate in slip rings I4. When current is caused to flo-w through coil II a magnetic field is set up with outer cup 4 .becoming one pole of the magnetic circuit and member I becoming the other pole. Similar poles are magnetically induced in cup 2 I, the polarity of the external surface of cup 2I being opposite in polarity to that of cup 4; and the polarity of the inner surface of cu-p 2I being opposite in polarity to that of member II). The proportion of iron and oil in the electromagnetic fluid is such that under centrifuging the iron will occupy only the cylindrical gap or peripheral space between member I0 and cup 2| and between cup 2I and the inner periphery of cup 4, with some small additional amount of powder substantially as shown. When current is passed through coil IIas heretofore described, the iron powder will be attracted through the magnetic path previously discussed, causing the powder to adhere to the outer periphery of I0, the inner periphery of cup 4 and to both peripheries of cup 2|, with a force dependent upon the strength of the current in coil I I, limited only by the design of said coil and the saturation 'point of the magnetic circuit.

With reference now to Figure 3, it will b-e seen that the mechanical arrangement of the parts is identical with -that shown in Figure 2, except that the amount of iron I5 has been decreased so that it fills but slightly more than the space between the cylindrical gap or outer periphery of cup 2I and the inner periphery of cup 4. This modification does not transmit as much torque for a given configuration of clutch as does the filling shown in Figure 2, but where high speed operation is required it transmits far less rotational drag between shaft 8 and shaft 3, when the coil I I is deenergized.

The previous practice with respect to the ironoil has been to first make up a mixture of a predetermined proportion of magnetic particles to fiuid, and then to use this mixture to fill the clutch. This resulted in a random amount of solid matter, in practice, a surplus of iron particles always being provided, because, if a very thin mixture were to be used, so that there were not enough particles to fill the gap, only a small amount of force could be transmitted, therefore a fairly thick mixture was always used. In any case, the previous practice entirely failed to consider the packing effect due to the great head of surplus metallic particles. When this is amplified by the effect of centrifugal force at high rotational speeds, it will be apparent that a very great improvement in the packing effect can be obtained by using no more than enough particles to clothe work. Very few of the particles are lost in a well-designed clutch, even after long use of the clutch, because they tend to stay in place; and even where a sufiicient number of particles may migrate to require special precautions to eliminate the possibility of their harming the bearings, these errant parti-cles are too few in practice to appreciably affect the operation of the clutch or to appreciably reduce the effective number of particles remaining in the clutch. However, there is some loss of oil during prolonged operation of the clutch, tending to dry it out.

In the past, it has been the practice to add more of the original mixture when the clutch appears to be getting dry. This of course still further increases the ratio of metal particles to oil in the clutch and still further increases the head of iron particles, and the tendency to pack will become more pronounced. In accordance With my invention only oil is added if the clutch appears to be drying out, and the quantity of metal particles remains unchanged. When dry paramagnetic particles alone are used the oil leakage problem does not arise.

The essential feature of my invention is therefore that the amount of metal particles put into each clutch is measured out for that particular clutch and enough oil is added to fill the rest of the available space, if oil is to be used. While this may appear to be very simple, it involves a radical departure from both the thinking and the procedure of the prior art, which first determined a ratio of metal particles to fluid, and then filled the clutch with a mixture having this ratio, and thus provided no correct determination of the proper amount of magnetic material essential to `provide both efficient operation and absence of packing. It would appear that the correct proportion would sometimes be attained by chance, but even this did not occur in practice because the mixtures used practically all provided too `much iron, and even if the correct amount were to be used by pure chance the first time, the practice of adding more mixtures subsequently, insured an oVersup-ply of metal particles eventually.

I claim;

l. A magnetic fluid clutch comprising two relatively movable members between which force is to be transmitted, said members having respectively spaced, opposed, cylindrical, coaxial, surfaces, said surfaces defining a cylindrical gap, a material comprising paramagnetic particles and a liquid in said gap, enclosure means for the ends of said gap constructed to retain said material in said gap and providing at least one radially extending gap joining into said cylindrical gap; said liquid only in said radially extending gap; and means for subjecting said paramagnetic particles to the action of a magnetic eld to control the transmission of force between said relatively movable members.

2. A magnetic fluid clutch comprising two aligned rotatable shafts, a coaxial cylindrical member fixed on the end of one shaft and defining a cylindrical container having end walls and a cylindrical inner surface, an aperture in the end wall remote from said one shaft, the second of said shafts extending through said aperture, a second cylindrical member fixed to the end of said second shaft within said cylindrical container and having an outer surface spaced from said inner surface, means for maintaining a magnetic field in the space between said surfaces, a quantity of paramagnetic particles in the space between said cylindrical surfaces, said quantity being substantially sufficient to extend from said cylindrical inner surfaces radially inward a distance corresponding to the distance between said opposed surfaces, and a quantity of fluid lling the remaining space within the cylindrical container.

3. The invention recited in claim 2 wherein said second cylindrical member is in the form of a second cylindrical container having an inner cylindrical surface and one open and one closed end, and a third cylindrical member fixed to and coaxial with said first member, projecting into said open end and having a cylindrical outer surface, said first and third cylindrical members defining a gap into which said second cylindrical member extends, and radial gaps between the ends of said cylinders.

4. The invention recited in claim 3 wherein the closed end of said second cylindrical container is provided with at least one aperture to permit circulation of the fluid.

5. A magnetic clutch comprising two relatively movable members between which force is to be transmitted, said members having respectively spaced, opposed, cylindrical, coaxial surfaces, said surfaces dening a cylindrical gap; inclosure means'for the ends of said gap and providing at least one radially extending gap joining into said cylindrical gap, a quantity of paramagnetic particles in said cylindrical gap, said quantity being limited to an amount sui'licient to fill said cylindrical gap, and means for subjecting said paramagnetic particles to the action of a magnetic field to control the transmission of force between said relatively movable members.

6. A magnetic clutch comprising two relatively movable members between which force is to be transmitted, said members having respectively spaced, opposed, cylindrical, coaxial surfaces, said surfaces dening a cylindrical gap, a fluid material comprising paramagnetic particles and oil in said gap, enclosure means for the ends of said gap constructed to retain said fluid material in said gap and providing at least one radially extending gap joining into said cylindrical gap, oil only in said radially extending gap, and means for subjecting said paramagnetic particles to the action of a magnetic field to control the transmission of force between said, relatively movable members.

'7. A magnetic clutch comprising two relatively movable members between which force is to be transmitted, said members having respectively spaced, opposed coaxial surfaces, said surfaces defining a cylindrical gap, a quantity of contiguous discrete paramagnetic particles in said gap, enclosure means for the ends of said gap constructed to retain said particles in said gap and providing at least one radially extending gap joining into said cylindrical gap, said quantity of paramagnetic particles being limited to an amount sufficient to substantially ll said cylindrical gap and means for subjecting said paramagnetic particles to a magnetic eld to control the transmission of force between said relatively movable members.

8. A magnetic fluid clutch comprising two relatively movable members between which force is to be transmitted, said members having respectively spaced, cpposed, cylindrical, coaxial surfaces, said surfaces dening a cylindrical gap, a quantity of contiguous discrete paramagnetic particles in said cylindrical gap, said quantity being limited to an amount suicient to substantialy ll the said gap, enclosure means for the ends cf the said gap constructed to retain the said particles in said gap, and means for subjecting the said paramagnetic particles to the action of a magnetic eld to control the transmission of force between said relatively movable members.

JACOB RABINOW REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,519,449 Findley Aug. 22, 1950 2,525,571 Winther Oct. l0, 1950 OTHER REFERENCES Technical Report 1213, National Bureau of Standards, Washington, D. C. 

